title: ACA12 is a deregulated isoform of plasma membrane Ca²⁺-ATPase of Arabidopsis thaliana.
abstract: Plant auto-inhibited Ca²⁺-ATPases (ACA) are crucial in defining the shape of calcium transients and therefore in eliciting plant responses to various stimuli. Arabidopsis thaliana genome encodes ten ACA isoforms that can be divided into four clusters based on gene structure and sequence homology. While isoforms from clusters 1, 2 and 4 have been characterized, virtually nothing is known about members of cluster 3 (ACA12 and ACA13). Here we show that a GFP-tagged ACA12 localizes at the plasma membrane and that expression of ACA12 rescues the phenotype of partial male sterility of a null mutant of the plasma membrane isoform ACA9, thus providing genetic evidence that ACA12 is a functional plasma membrane-resident Ca²⁺-ATPase. By ACA12 expression in yeast and purification by CaM-affinity chromatography, we show that, unlike other ACAs, the activity of ACA12 is not stimulated by CaM. Moreover, full length ACA12 is able to rescue a yeast mutant deficient in calcium pumps. Analysis of single point ACA12 mutants suggests that ACA12 loss of auto-inhibition can be ascribed to the lack of two acidic residues--highly conserved in other ACA isoforms--localized at the cytoplasmic edge of the second and third transmembrane segments. Together, these results support a model in which the calcium pump activity of ACA12 is primarily regulated by increasing or decreasing mRNA expression and/or protein translation and degradation.
authors.affiliation: Dipartimento di Bioscienze, Istituto di Biofisica del CNR, Sezione di Milano, Università degli Studi di Milano, via G. Celoria 26, 20133, Milan, Italy.
authors.forename: Margherita
authors.initials: M
authors.lastname: Limonta
authors.forename: Shawn
authors.initials: S
authors.lastname: Romanowsky
authors.forename: Claudio
authors.initials: C
authors.lastname: Olivari
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Bonza
authors.forename: Laura
authors.initials: L
authors.lastname: Luoni
authors.forename: Alexa
authors.initials: A
authors.lastname: Rosenberg
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Harper
authors.forename: Maria Ida
authors.initials: MI
authors.lastname: De Michelis
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D055162:Biocatalysis / Q000187:drug effects; D015153:Blotting, Western; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology*; D005298:Fertility / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D030821:Plants, Genetically Modified; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D002147:Calmodulin; D007527:Isoenzymes; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate; C587967:ACA12 protein, Arabidopsis; D000252:Calcium-Transporting ATPases